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SYNTHESIS, CHARACTERIZATION AND LUMINESCENCE STUDIES OF TERBIUM (III) COMPLEXES**

Abstract

Lanthanide(III) complexes are of significant interest due to their characteristic photoluminescence, which enables applications in light-emitting diodes, biomedical imaging, and optical amplification. Luminescence intensity can be enhanced by coordinating the metal center with organic ligands capable of strong UV absorption and efficient energy transfer through the antenna effect. In this study, the sodium salt of mefenamic acid—an organic acid with a conjugated system and two coordination sites, was employed to synthesize a terbium(III) complex. The reaction of Tb(NO₃)₃·6H₂O with sodium mefenamate (C₁₅H₁₄NO₂Na) in distilled water at room temperature, using a 1:3 metal-to-ligand molar ratio, produced a white solid in high yield. The product was characterized using spectroscopic techniques and CHN analysis, and the results support the formulation of Tb(C₁₅H₁₄NO₂)₃·2H₂O. The complex is soluble in DMSO but insoluble in most other polar and nonpolar organic solvents. Fluorescence studies in DMSO revealed an excitation maximum at 376 nm and an emission maximum at 545 nm. The FTIR spectrum displayed characteristic ligand bands with slight shifts upon coordination, along with a weak broad absorption near 3300 cm⁻¹ indicative of coordinated water molecules. CHN analysis values were consistent with the proposed composition, further confirming the formation of Tb(C₁₅H₁₄NO₂)₃·2H₂O.

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